1. Field of the Invention
The present invention relates to a dual loop type data highway system, and more particularly to a dual loop type data highway system including dual loops, a plurality of data transmitting/receiving stations connected to those loops and a control station for permitting data transmission/reception between selected data transmitting/receiving stations by polling the data transmitting/receiving stations.
The data highway system is a loop transmission system commonly used in a production management and a calculation control in a variety of fields such as iron and steel industries and chemical plants.
2. Description of the Prior Art
A prior art data highway system has been constructed to include a single control station and a plurality of data transmitting/receiving stations connected in a loop so that a computer and terminal units are connected through the respective data transmitting/receiving stations. In such a data highway system, in order to increase the effective transmission rate, an optical fiber may be used as the transmission loop. In such a system, the control station and the data transmitting/receiving stations carry out various transmission controls by means of microprocessors. Thus, if the transmission rate exceeds 10-20 M bits per second for example, it will become unfeasible to carry out such processings. As a result, the transmission control has to be carried out by their own hardware and hence the amount of hardware at each of the data transmitting/receiving stations increases. In order to avoid such a problem, two loops may be provided and two data transmitting/receiving stations which carry out the transmission control are provided so that the entire loop is duplexed to increase the effective transmission rate. In this method, however, a considerable increase of the amount of hardware is unavoidable.